Influence of kaolin and coal fly ash addition on biomass ash deposition in an entrained flow reactor

The ash deposition behavior when firing different biomass (pulverized wheat straw, wood, bark, and leaves), with and without K-capture additives (kaolin and coal fly ash) was investigated through combustion experiments in the DTU (Technical University of Denmark) entrained flow reactor (EFR). In terms of deposit formation, the K- and Cl-rich Danish wheat straw proved to be the most problematic fuel, while milled wood pellets, leaves, and bark had significantly lower deposition propensities. Kaolin and two types of coal fly ash (Al- and Si-rich) were used as K-capture additives, and the results showed that with a fuel-K/additive-Al molar ratio of 1.0, the deposition propensity of wheat straw combustion was significantly reduced. However, the deposition propensity of the combustion of milled wood pellets did not change significantly with the addition of additives. ICP-elemental analysis of the deposits and fly ash samples showed that the water-soluble K content in the deposits and fly ash was significantly reduced for both wheat straw and wood pellet combustion. In comparison with the data from previous experiments, where pure K-salt reacted with solid additives, kaolin captured KOH more effectively than real biomass combustion. For coal fly ash, an opposite tendency was observed, i.e., it captured K more effectively under real biomass combustion conditions than under pure KOH reaction conditions.